Field of the Invention
One disclosed aspect of the embodiments relates to a radiation imaging apparatus and a radiation imaging system.
Description of the Related Art
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-525983 discusses a radiation imaging apparatus including a holding unit (sample-and-hold circuit) in which each pixel of a sensor array holds a signal (hereinafter, referred to as a signal S) according to an amount of emitted radiation. Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-525983 further discusses an imaging apparatus in which each pixel obtains signals (hereinafter, referred to as signals S1 and S2) with two sensitivities, for example, and the signals S1 and S2 are used to generate image data. According to Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-525983, each pixel is provided with two holding units. The signals S1 and S2 obtained with the respective sensitivities can be held in and individually read from the respective holding units.
Japanese Patent Application Laid-Open No. 2012-085124 discusses a radiation imaging apparatus including a plurality of pixels, a selection unit, a control unit, and a determination unit. The pixels according to Japanese Patent Application Laid-Open No. 2012-085124 each include a conversion unit configured to convert radiation into a signal, a holding unit configured to perform holding of the signal from the conversion unit, an output unit configured to output the signal held in the holding unit, and a reset unit configured to perform resetting of the conversion unit. The selection unit according to Japanese Patent Application Laid-Open No. 2012-085124 performs an operation for selecting a pixel from which the held signal is to be output, and outputs the held signals from the plurality of pixels. The control unit according to Japanese Patent Application Laid-Open No. 2012-085124 controls the plurality of pixels so that the resetting is concurrently performed on the plurality of pixels based on a signal indicating timing of generation of the radiation, and so that the holding is concurrently performed on the plurality of pixels. The determination unit according to Japanese Patent Application Laid-Open No. 2012-085124 determines, when the resetting based on the signal indicating the timing is performed, whether the selection operation on the plurality of pixels (pixel circuits) based on a signal indicating the immediately previous timing ends. In Japanese Patent Application Laid-Open No. 2012-085124, if the determination unit determines that the selection operation does not end, the selection unit stops the selection operation with part of the plurality of pixel circuits being left undone, and resumes the selection operation on the part of the pixel circuits after the resetting is performed by the control unit. According to Japanese Patent Application Laid-Open No. 2012-085124, such control and such a selection operation enable moving image capturing at a frame rate higher than that of the radiation imaging apparatus according to Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-525983, and with suppressed artifacts due to the resetting.
However, the radiation imaging apparatuses according to Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-525983 and Japanese Patent Application Laid-Open No. 2012-085124 are not given due consideration about possible artifacts in an image of the first frame after a start of moving image capturing.
In some cases, an artifact may thus occur in the image of the first frame after the start of moving image capturing. For example, according to Japanese Patent Application Laid-Open No. 2012-085124, the selection operation in a period between resetting and holding, i.e., in an accumulation period of the conversion unit differs between the first frame and the second and subsequent frames. There has thus been a possibility of an artifact based on such a difference.